The invention pertains to the use of fluid droplet expulsion techniques for the fabrication of various devices. Particular embodiments of the invention have application to making color liquid crystal displays.
Demand for liquid crystal displays and in particular color liquid crystal displays is increasing with the spread of portable personal computers, handheld computer and organizer devices and many other electronic devices. Current liquid crystal display fabrication techniques have relatively low yields, especially for large, color liquid crystal displays. Manufacturers of existing color liquid crystal devices often reject a significant percentage of the devices that come off of the assembly line. Such a low yield makes the per unit fabrication cost of each device relatively high. It is desirable to increase the yield and decrease the cost associated with the fabrication of color liquid crystal displays. In particular, it is desirable to reduce the cost associated with the fabrication of color filters.
Various methods have been proposed for the fabrication of color filters suitable for liquid crystal displays. Such techniques include: (i) a pigment dispersion method, where a photosensitive layer of a dispersed pigment is formed on a substrate and patterned to form a color pattern; (ii) a dyeing method, where a polymer layer is formed on a substrate, patterned using photolithography and then dipped into a dye bath to add color; (iii) an electrodeposition method, where a transparent electrode is patterned into a substrate and is dipped into an electrodeposition solution containing a pigment, a resin and an electrolytic solvent; and (iv) a printing method, where a pigment is dispersed into a thermosetting resin, the dispersion is printed and then cured by heat. These techniques typically require three separate repetitions to fabricate red, green and blue color filters, making color filter fabrication relatively time consuming and expensive. The large number of steps associated with these techniques also tends to decrease the production yield.
A relatively recent technique for the fabrication of color filters involves the use of inkjet nozzles to expel curable ink directly onto the transparent substrate of the liquid crystal display. Red, green and blue ink may be applied in a single pass of the inkjet head or in multiple passes. After the ink of various colors is applied, the ink is cured on the substrate to form color filters.
Inkjet techniques have various problems related to the coalescing of adjacent ink droplets and/or the mixing of various colored ink droplets on the surface of the transparent substrate prior to curing. This coalescing and mixing of adjacent ink droplets in an inkjet process may be due to a myriad if factors, including without limitation: poor registration of the inkjet head; surface energy characteristics of the ink droplets and the transparent substrate; and/or emission of ink droplets from the inkjet head at inconsistent or off center trajectories.
A number of techniques aimed at combating the coalescing and mixing of ink during inkjet fabrication of color filters include Japanese Patents No. JP6,347,637 (Isao) and No. JP10,197,715 (Hirohide et al.) and U.S. Pat. No. 5,817,441 (Iwata et al.), U.S. Pat. No. 5,948,577 (Nakazawa et al.), U.S. Pat. No. 5,908,721 (Emoto et al.) and U.S. Pat. No. 6,022,647 (Hirose et al.).
Isao describes the use of an ink having certain surface tension properties, which is expelled between barriers containing a flourine-based water repellent (hydrophobic) and oil repellent (oleophobic) agent.
Hirohide et al. teaches the photolithographic formation of light shielding barriers containing a hydrophobic/oleophobic compound having certain surface energy, and then using inkjet to expel ink between the light shielding barriers.
Iwata et al. describes the photolithographic formation of a pre-cured hydrophobic black matrix barrier pattern, followed by the inkjet application of ink to the regions between the black matrix barrier pattern.
Nakazawa et al. describes the formation of a light shielding black matrix barrier, followed by the inkjet application and curing of colored ink.
Emoto et al. describes a chemical formulation for a light shading colored resin that is applied to the substrate as a barrier.
Hirose et al. describes a technique for fabricating a color filter comprising forming barriers on the substrate, using inkjet to apply a certain volume of ink having certain surface tension properties into the regions between the barriers and curing the ink to form color filters.
Each of these prior art techniques describes the application of ink droplets directly to the substrate by ejecting the ink droplets from the nozzles of an inkjet head. An enduring problem with the expulsion of ink from ink jet nozzles, is that nozzles can fail or become clogged. For these and/or other reasons, ink droplets emitted from inkjet nozzles may be emitted at off-center or inconsistent trajectories. These deficiencies with inkjet expulsion may cause ink droplets to be ejected to improper locations on the substrate, cause ink droplets to coalesce on the substrate and/or lead to other defects in the fabrication of the color filters for liquid crystal displays. These drawbacks with the prior art techniques tend to increase the likelihood of fabrication errors and/or defects, which may lead to poor yield.
Even in circumstances where ink droplets are properly expelled by the nozzles of inkjet heads, these prior art techniques are limited by the spreading of ink droplets on the surface of the substrate and the overall resolution of current inkjet technology. These drawbacks with the prior art limit the availability of the prior art techniques for finer resolution (i.e. smaller pixel) applications.
There is a need for cost effective methods and apparatus for the precision formation of color filters for use in displays that ameliorate at least some of the difficulties associated with currently available techniques.
One aspect of the invention provides a method for fabricating color filters for a display on a surface of a substrate. The method comprises ejecting fluid droplets from one or more fluid droplet sources onto a transfer surface and transferring the fluid droplets from the transfer surface to the substrate by bringing the fluid droplets on the transfer surface into contact with the substrate.
The transfer surface may comprise a periodic pattern in at least one dimension. The method may comprise adjusting the spatial registration of the fluid droplets while they are on the transfer surface through an interaction between the fluid droplets and the periodic pattern on the transfer surface.
The periodic pattern on the transfer surface may comprise a plurality of fluid-droplet-retentive regions on an otherwise less fluid-droplet-retentive surface.
The method may comprise modifying the rheological characteristics of the fluid droplets and/or the size of the fluid droplets while the fluid droplets are on the transfer surface.
The method may comprise single or multiple passes between the fluid droplet sources and the transfer surface and/or single or multiple passes between the transfer surface and the substrate.
The method may comprise curing the fluid droplets on the substrate. Curing the fluid droplets may occur in one or more stages.
Another aspect of the invention involves a method of fabricating organic light emitting diodes (OLED""s). Such a method comprises ejecting fluid droplets from one or more fluid droplet sources onto a transfer surface and transferring the fluid droplets from the transfer surface to the substrate by bringing the fluid droplets on the transfer surface into contact with the substrate.
Another aspect of the invention involves a method of fabricating polymer semiconductors. Such a method comprises ejecting fluid droplets from one or more fluid droplet sources onto a transfer surface and transferring the fluid droplets from the transfer surface to the substrate by bringing the fluid droplets on the transfer surface into contact with the substrate.
Further aspects of the invention and features of specific embodiments of the invention are described below.